The inventions described below were developed to aid in the treatment of prostate enlargement and/or prostate cancer. Prostate enlargement, also known as benign prostate hyperplasia or benign prostate hypertrophy, is a common affliction among older men. The condition involves swelling of the prostate. The prostate surrounds the urethra, or urinary tract, and swelling of the prostate prevents passage of urine from the bladder. Benign prostate hyperplasia is uncomfortable because it makes urination difficult or impossible, The condition is also dangerous because it can lead to infection of the bladder and kidneys, and severe cases may lead to death.
Prostate cancer is also a common affliction among older men, and may lead to many of the same symptoms as benign prostate enlargement. Prostate cancer is more dangerous in that it may spread to other organs and is often fatal. Early treatment can reduce the risks of death due to prostate cancer.
A surgical cure for prostate enlargement is called resection. Resection can be accomplished by cutting away a large portion of the prostate gland. The operation can be performed by cutting through the skin to expose the prostate gland, and using scalpels to cut into the prostate. Preferably, resection is accomplished from inside the urethra, using a resectoscope inserted through the penis. The resectoscope includes an endoscope for visual observation and a resecting loop which a surgeon uses to scrape and gouge away the prostate gland from the inside.
Prostate enlargement can be treated with heat treatments such as hyperthermia or thermotherapy, cold treatment (hypothermia or cryotherapy), and ablation. It has long been known that heating a swollen prostate gland can lead to a decrease in swelling and eventual relief from the condition. Heat treatment denaturizes the proteins in the prostate tissue, like a slow cooking of the tissues. The biological effects of heat treatment and the appropriate thermal dosage are discussed in more detail in articles such as Terai, et al., Transurethral Microwave Thermotherapy For Benign Prostatic Hyperplasia, International Journal of Urology 24 (March 1995) and Pow-Sang, et al., Thermocoagulation Effect Of Diode Laser Radiation In The Human Prostate, 45 Urology 790 (May 1995), but it is sufficient for the purposes of this disclosure to understand that application of heat at sufficiently high temperature for sufficient lengths of time to destroy some or all cells in a portion of the prostate gland eventually produces a therapeutic effect.
Devices for heating the prostate are illustrated, for example, in Edwards, et al., Medical Probe Device and Method, U.S. Pat. No. 5,366,490 (Nov. 22, 1994), which shows a device for application of RF or microwave energy into the prostate while protecting the prostatic urethra from damage during the treatment. Hyperthermia treatment, as the term is generally used, is accomplished in the temperature range of 40-60.degree. C. Thermotherapy, as the term is generally used, is accomplished by heating the prostate above 60.degree. C. Both heat treatments have been beneficially used in the treatment of prostate enlargement.
After heat treatment, the prostate gland will be partially destroyed. Thermal necrosis, thermocoagulation, denaturization, and other such terms are used to describe the thermal damage done to the prostate gland. The prostatic urethra will also be partially destroyed. The prostate gland and the prostatic urethra swell in response to the burn caused by the heat treatment, and this immediately causes acute blockage of the urethra. The prostate gland and prostatic urethra eventually heal, over several weeks or months, typically about three months after heat treatment.
During the healing period, much of the prostate and prostatic urethra that were damaged by the heat treatment are re-absorbed by the body through the blood vessels supplying the area. However, significant portions near the urethra slough off the urethra wall and fall into the urethra. Sloughing causes acute blockage of the urethra. Thus, during the post-operative healing period, swelling and sloughing cause acute blockage of the urethra, leading to extreme discomfort and clinical danger to the patient. After healing, the prostate will be smaller than before heat treatment and will not force closure of the urethra. The condition of benign prostate hyperplasia is essentially cured. Prostate cancer can also be treated successfully with similar heat treatments, usually in combination with chemotherapy or radiation treatment.
It has recently been proposed to use stents to support the urethra and keep it open despite pressure from the swollen prostate. The Prostacoil.TM. temporary intraprostatic stent, marketed by Instent, Inc. of Eden Prairie, Minn., is an example of a stent adapted for use in the prostatic urethra. The stent includes an anchoring section and a prostatic section, and is placed with a delivery catheter shaft through the urethra. The stent is used long-term, for patients temporarily or permanently unfit for surgery.
A wide variety of stents have been proposed for use in various applications. Intravascular stents and coronary stents such as the Palmaz-Schatz stent illustrated in Palmaz, have been used to treat occlusions of blood vessels. A commonly suggested material for making stents is pseudoelastic and/or shape memory alloys such as Nitinol. For example, Sugita, Catheter, U.S. Pat. No. 4,969,890 (Nov. 13, 1990) proposes use of a shape memory alloy for an intravascular stent, and shows a device for percutaneous delivery of the stent to an occluded stenotic region of a blood vessel. Harada, et al, Method of Implanting a Stent Within a Tubular Organ of a Living Body and of removing Same, U.S. Pat. No. 5,037,427 (Aug., 4, 1991) proposes use of a two-way shape memory alloy stent in a blood vessel. Two-way shape memory is useful in a stent, according to Harada, to allow removal of the stent. As explained in Harada, it is not possible to remove a one-way shape memory stent after implantation. Harada proposes use of two-way shape memory stent with a hot, large diameter shape which holds a blood vessel open and a cold, small diameter shape which can be moved within the vessel and removed. Harada also discloses a device for percutaneous placement of the stent. Dotter, Transluminally Placed Expandable Graft Prosthesis, U.S. Pat. No. 4,503,569 shows the use of shape memory alloy stent proposed for use in blood vessels. Each of these references use saline solution injected through a catheter to control the temperature of the stent, thereby controlling the shape of the stent.
Stents may be left in blood vessels permanently, and are usually implanted for permanent use. The risk of infection around the stent in a blood vessel, or movement of the stent within a blood vessel, are somewhat limited by the environment. In the urethra, however, the risk of infection is high, and movement within the urethra may be caused by urination or ejaculation, especially if the prostate gland shrinks in response to treatment. Thus, there is a limit to the amount of time a stent may be left implanted in the urethra before infection sets in or migration occurs.